Thursday May 27th.

Now everything is ready for the concrete truck. The truck will arrive Monday morning at 7 am. Wow, I'm excited!

Here is a picture of the hole with rebar cage and support for the sleeve. The sleeve is a piece of bended sheet metal in which the ground post will slid in. It absolutely essential that the sleeve is positioned exactly vertically, or the mast will lean.

Plate and load capacitor installed.

Toroiods for 160 meter (the big one) and L-coil

And now a little side track. This is my new 12 meter antenna mast to replace the roof mountings. Eventually I will have a Steppir in the top.

The 7 meter bottom section lying on the ground. The 5 meter top extracts by means of a winch.

Rotor cage

Ground post. When retracted, the mast fold over the ground post for easy access to the antenna mount.

The dig! It will be 1x1x1 meter when ready!

Work in progress. The making of an air wound pi coil!

It has been a while since last post. The build has not stalled but the process has been very slow lately. The reason is that I have had too much work to do the last months. I have not been able to spend any time in the work shop. However, this Easter weekend gave me the opportunity to to do some work. The goal for this weekend was to make the 30 to 80 meter pi coil. The raw material is 3 mm copper wire which should be more than adequate for 1 KW in SSB service. Further on, this size should be able to withstand continuos service as well

The completed coil mesures 70 mm OD, 84 mm in length and has a total number of 18 turns. The measured inductance is 11,18 micro Henry and the calculated value is 12, 54 micro Henry. The needed inductance for the Pi-L tank is 11,04. So the result is perfect!

First step of the coil making. About 40 turns coiled up on a 60 mm steel tube. I used only 18 turns.

Four polycarbonate ribs are cut to size. They will support the coil and keep the pitch of the turns through out the length of the coil. Polycarbonate (Lexan) is a very good plastic materiel, far superior to the more common acrylic. It is a lot easier to work with machine tools since it does not splinter as easy.

The supporting ribs are drilled to accommodate the coil.

This is the time consuming part! The polycarbonate ribs are threaded on the coil, turn by turn!

The coil is ready! Nice and shining. It almost looks factory made.

After making this 11 micro Henry coil I realize that the amplifier housing does not have room to accommodate the 160 meter pi coil nor the L-coil for all bands if I make them as traditional air wound coils. For this I need to investigate how to use toroids in high power coil design!

Gu74B amp project progress!

It was I while ago I had some updates here. This is because of several reasons; one of them I will tell about further down. The other reasons is that I had a hard time finding meters for a good price. I searched Ebay and other sites hoping for some nice looking meters to show up for a bargain. Finally I gave up and bought two brand new SIFAM meters. Althoug they look nice, they were also very expensive. The other reason for the delay has been my fear of making square holes! Back in the days I never succeeded, but this time I actually got it right! The secret? The right tools and patience!

Here is the front panel with almost all holes done. What is missing are three shaft holes for the tank capacitors and band switch. As you can see, I succeeded very well with the square holes. The meters are beautifully aligned and so are the rocker switches. The over all finnish of the front panel may look ugly in this phase. But you should understand that the grey surface with blue lines is a protective plastic film on the aluminum. Once taken off, I expect a shiny and bright aluminum surface. I plan to anodize and print labels on it. Does anyone know where I can get the sheet anodized in the Stockholm area? Another alternative is to order a custom made front panel from the guys at Front Panel Express. It is very easy, you draw your panel with their software and you get the price instantly. You then upload the file to there workshop in Germany and about a week later you get a beautiful anodized front panel with holes and prints for about €120. But, I don't think that will be necessary!

Of course the panel meters are back-lit! (I will customize the scales later).

Detail picture of the wiring. I only use teflon or silicon rubber insulated high temperature wire. It is wonderful to work with, no accidentally melted plastics while soldering. But more costly!

This is the 900 volt AC post. I could not find high voltage rated posts, so this is a 600 volt post that I elevated from the chassis by two pillars. Will I have a flash over between the connectors here? I don't think so. Here it is "only" 900 volts AC and about 8-9 mm between the cables. But I'd be happy for any comment on this. Also the teflon wire is only rated at 600 volts. To increase the insulation factor I have led the cable through a piece of teflon tubing. Maybe this is over-kill, but it feels good!

I've got some comments about the RF deck being empty so I thought I might upload some pictures of things that are going in there in the next couple of months. The main reason for the RF deck being empty is that I'm bent on having completed the PS 100% before starting with the fun parts. Back in the days when I built 813 amplifiers I always started withe the big tubes and capacitors and when it finally was time for the PS I was so eager to get it working that the PS ended up being a very hasty work. But I have learnt that a good PS is really one of the most important things both from a performance and a security stand point. Hence, I will not go into building the RF deck until the PS is fully operational. But, in the mean time, enjoy some pictures of the "big things":

Tank coil for 10-20 meters. I wound with 4,5 mm copper tubing

Very nice NOS ceramic band switch with silver plated contacts. I got from Ralf at QRO-shop in Germany. (http://www.qro-shop.com/)

Tune capacitor. 100o pF, 1,5 mm spacing. I bought it second hand from a amateur in Skåne.

Custom made Plate capacitor from Ham Center in Italy. 23-320 pF, 3 mm spacing.

A weeks work on the GU74B Kilowatt amp project

The work has slowed down somewhat since the last post due to other things. But last week I felt that it was necessary to start again. I'm starting to realize that this is actually a hugh project! Some things just takes a lot of time and you don't really see any progress. But this undertaking is like any big project; it is about commitment and persistence! It is not always a perfect day to do some work on the amplifier. But when you feel like that you have to go there and at least do something. Otherwise there is a big risk that the project ends up on the shelf. I'm, however, determined that this is not going to happen.

Ok, let's g over to pictures and tell what has been going since the last post!

Overview of the amplifier. PSU compartment and RF deck.

From left to right:

The first boards are the two stacked G3SEK tetrode boards. Mounted on the sides are two power resistors that are part of screen grid circuit.

The board in the middle is the new redesigned voltage doubler. When the voltage doubler was completed the first time i realized it was too big and heavy (see earlier post for picture). With 10 400 volt NOS capacitors it was so heavy that the circuit board was bending under the weight. The new board is designed around 8 450 volt low-profile capacitors I found on Mouser. They were expensive at almost 6 Euros a piece. But it was well worth it, given the fact that the result made it possible to build everything smaller which in turn will make it possible to accommodate a second HV transformer later on.

To the right you can see a smaller toroid that carries 18-0-18 volts for the control boards and relays. Also here you can see two hefty relays with associated power resistor for HV control and soft start.

Side view of the PSU

On this side view you can see that everything is actually built on two floors. The two stacked G3SEK boards are clearly visible with a large heat sink beneath. Then the voltage doubler and then, to the far right transformer for control voltages and power entry module.

On the second floor I have bolted the HV transformer to the bottom of the chassis together with terminal blocks and 230 volt mains wiring. As you can see here, there is room for another toroid exactly like the first one, which would make it possible to upgrade the system to 1600 VA input instead of the current 800 VA. 800 VA input is basically fine for 1 Kw+ PEP in CW or SSB. But should I like to operate in 100% duty cycle I need more iron! I don't know if I ever go there, but it is nice to have the option.

Next step now is to hook up the G3SEK boards to 18 volts and start testing it. Now there is also an awful lot of boring wiring to do. I think next post will come sometime during the christmas holidays.